Fatigue Mechanism in Iron at Ultrasonic Frequency

Abstract

A metallographic study compares the fatigue mechanism in low‐carbon iron subjected on the one hand to cycles of strain at an ultrasonic frequency of 17 000 Hz and on the other to 1700 cpm, the relative low order employed in usual engineering tests. It is found that the ultrasonic frequency can produce fatigue cracks at strain amplitudes much smaller than those which up to now have been regarded as safe at low frequency. Further, whereas small amplitudes at low frequency spread abnormal deformation primarily in grain boundaries, those at ultrasonic frequency concentrate it in a relatively few isolated slip bands thereby, it is suggested, heightening their damaging effects.